Electrostatic charger apparatus



Nov. 8, 1960' F. A. CROSKEY ETAL ELECTROSTATIC CHARGER APPARATUS FiledOct. 4. 1954 4/ 4% SUP/01V L l 2 Sheets-Sheet l INVENTORS .7 l'lfar/f 3W??? 112 21142511 ORNEY Nov. 8, 1960 F. A. CROSKEY ETI'AL 2,959,353

ELECTROSTATIC CHARGER APPARATUS Flled Oct. 4, 1954 g s t -s t 2 6g! 7MI. ATTORNEY United States Patent ELECTROSTATIC CHARGER APPARATUS FrankA. Croskey, Detroit, and Charles Derwood Tuttle,

Wyandotte, Mich., assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware Filed Oct. 4, 1954, Ser. No. 459,968

8 Claims. (Cl. 239-15) This invention relates to electrostatic chargingapparatus for charging particles of coating material and, moreparticularly, to electrostatic hand spray coating installations and to ahigh tension circuit breaker and associated control therefor.

In one aspect of the present invention, the invention has for an objectto provide an improved electrostatic hand spray installation which, byreason of the form of charging system employed therein, enables the useof a comparatively low voltage and current for charging particles ofcoating material without danger of harm to the operator.

In another aspect, the invention has for an object to provide animproved electrostatic hand spray installation in which the intensity ofthe electrostatic field and the particle charging efficiency areindependent of the distance of the charging electrode and/ or theoperator from the articles to be coated.

In a related aspect, the invention has for another object to provide animproved electrostatic hand spray installation in which the operator,spray gun and charging system may be located beyond the range ofbackspray from the articles and which permits the operator to be removedsufiiciently from the articles so as to avoid the need for specialprotective structures limiting the approach of the operator to thearticle.

Still another object is to provide an improved electrostatic hand sprayinstall-ation having a common operating source located at the gun forcontrolling both the flow of particles of coating material and theremote applica tion and interruption of the high tension voltage to thecharging or depositing electrodes.

A further object is to provide an improved form of high tension breakerand remote operated control there-- with the present invention for anelectrostatic spray paint 7 ing installation; Fig. 2 illustrates a spraygun and a form of electrostatic paint charging system including aportion of the control apparatus of the present invention;

Fig. 3 is a sectioned elevation view of an electric circuit breaker inaccordance with the present invention; and Fig. 4 is a transverse viewtaken in the direction 4--4 of Fig. 3.

, Referring to Fig. 1 of the drawings, there is shown a high voltagepower supply unit 10, which is energized Patented Nov. 8, 1960 from alocal alternating current source of supply over conductors 12 and 14.The output of the power supply may be in the order of, say, 40kilovolts, and is applied over cable 16 through an air actuated circuitbreaker, indicated generally at 18, to cable 20. Cable 20 is connectedto one of the charging electrodes of an electro-' static spray paintingcharging system 22, the other element of which is connected back to thepower supply unit over conductor 24. The power supply unit 10 may beofthe RF oscillator type shown in copending United States application,Serial No. 234.312, filed June 29, 1951, in the names of Grayland T.Larsen and Arthur T. Lausten, assigned to the present assignee, and ispreferably provided with the current limiting are preventing feature ofthat application.

The circuit breaker 18 comprises, in general, a stationary high voltagecontact 28, a piston or slide rod 30, a conducting cylinder 32 thatsurrounds the piston and a ground stop contact 34 which is connected toground over conductor 36. The piston 30 is actuated from a source 41 ofcompressed air supplied through an airline 40 to a solenoid-actuated airvalve 42 through which the air is selectively applied to either one of apair of airlines 44 and 46 that communicate with the cylinder 32 onopposite sides of the piston 30.

The valve 42 is actuated by a low voltage split solenoid coil 48 whichis selectively electrically energized over conductors 50 and 52 throughthe contacts of a low voltage control relay 54 from a step-downtransformer 56 connected to the local alternating current supply. Ajumper (not shown) within the housing of the power supply unit 10connects line conductors 12, 14 to conductors 57, 58, which are shownconnected to the primary winding 59 of the step-down transformer 56, thehigh or ungrounded side of the low voltage secondary winding 60 of whichis shown connected to the branched sole noid conductors 50 and 52through a normally open set of contacts 61 and a normally closed set ofcontacts 62 of the control relay 54. One side of the actuating coil 64of the control relay 54 is connected in an energizing circuit whichincludes conductor 65 connected to the positive six-volt side of thefilament of one of the low voltage operating tubes, such as theoscillator tube 68, contained within the power supply 10. The other sideof the control relay coil is connected by conductor to ground through amicro-switch 72 that is mounted on the handle of the spray gun 74grasped by the operators A pilot light 75 may be connected across theactuating coil of the control relay to indicate the closed condition ofthe switch 72, which may be of the common snap action over-centervariety.

The spray gun shown in Fig. 2 is of a common com mercially availablevariety and is provided with a handle 76 and a manually operated trigger77 that is pivotally mounted on a pivot shaft 78 which passes throughthe body of the gun. Trigger 77 actuates a needle valve 79 containedwithin the gun and simultane' ously controls the flow of atomizing airand paint which are admitted to the gun through air and paint supplylines 80 and 81, respectively. The paint or coating material is ejectedin particle form from the nozzle or spray tip 82 of the gun which may begrounded. t

In accordance with one aspect of the present invention, the pivot shaft78 for the gun trigger 77 mounts a cam 84 thereon which actuates themovable actuating element'- 86 of the micro-switch 72 also mounted onthe gun,- whereby both the flow of the material to be deposited and theoperation'o'f the circuit breaker 18 are controlled from acornmon'operating source. The cam 84 is adjustable and may be so mountedon pivot shaft 78 relative to the actuating element 86 of themicro-switch asrftg actuate the latter upon the initial movement oftrigger 77 to cause the application of the high tension voltage to theelectrodes of the particle charging system slightly in advance of thecommencement of the flow of the particle spray from the gun.

As best shown in Fig. 2, the nozzle end of the spray gun extends throughan Opening in an insulating shield' 90, which is detachably secured tothe gun and located between the handle and the spray tip thereof.Fastened to one edge of the shield and extending in the forwarddirection of the spray from the gun is a broad flattened currentcollector electrode 94 which constitutes one of the electrodes of aportable electrostatic charger system in accordance with the presentinvention. The other electrode is constituted by a plurality ofelongated attenuated or needle-like discharge electrodes 96 which arespaced from and are contained in a transverse plane extending generallynormal to collector electrode and to the direction of the particletravel from the gun, which may be connected to ground as shown inFig. 1. The needle electrodes are mounted in a suitable support 98,shown carried by and extending forwardly of the shield 90, and areadapted to be connected to the high tension breaker cable 20. Cable 20may be of the rubber-covered coaxial variety and is brought into thecharging system for connection to the discharge electrodes rearwardly ofthe gun to prevent the cable from being coated with paint from the gun.Conductor 24 may be rubber covered braided conductor that connectscollector plate 94 back to the power supply unit and may be at or a fewvolts above ground potential.

The spacing between the discharge electrodes 96 and the collectorelectrode 94 of the charging system employed in the present invention isin the order of some 2 /2 inches and permits the use of a potential forthe ionizing electrostatic field that is established between theseelectrodes in the order of 37 to 42 kilovolts at an operating current ofaround 40 microamperes. This magnitude of potential is considerablylower than that required by other electrostatic depositing installationsin which the electrostatic depositing field is formed between adischarge electrode located immediately forward of the gun and thearticle or workpiece to be coated located some 10 to 12 or more inchesdistance therefrom. Systems of the latter character requireelectrostatic field potentials upwards of 100,000 volts at operatingcurrents in the neighborhood of 200 microamperes, which are in a rangelikely to cause serious bodily harm to the operator who must be locatedclose to the discharge electrode and workpiece for satisfactoryoperation of systems of this character. In the present system, theworkpiece 100 forms no part of and is contained entirely outside of theelectrostatic charging field ,of the charging system employed herein sothat the operator may be located sufiicicntly distant from the workpieceto avoid backspray from and contact therewith without loss of paintingetficiency. In fact, it has been found that by locating the operator andspray gun further away from and to one side of the workpiece, the painttends to be deposited more uniformly and to wrap more completely aroundthe back surface of the articles to be coated.

The application of a high difference of potential between the dischargeneedles and the collector electrode effectively ionizes the atmospheretherebetween causing an electric wind in the form of a corona pointdischarge to emanate from the discharge needles. This discharge extendsa short distance from the needles-toward but less than the distance fromthe tips of the needles to the collector electrode-and effectivelyplaces a very high charge concentration on the surface of the particlesof coating material. This charge is substantially constant andindependent of the location of the spray gun from the articles to becoated.

The breaker 18.of :the present invention is shown more fully in Figs. 3and 4 and comprises a cabinet housing containing a plurality of spacedsupport blocks 112, 114, 116, 118 which are mounted on the base 120 ofthe housing, substantially as shown. The support blocks are composed ofsuitable insulating material such as polystyrene. Mounted in an end wall122 of the breaker housing is a coaxial cable connector 124 for thecoaxial cable 16 from the power supply unit 10. The end of the connectorwithin the housing receives one end of a polystyrene tube 126, the otherend of which is seated in a shallow counterbore provided in one face ofblock 118. Tube 126 surrounds a central conductor 128 which is connectedat one end to the central conductor of the cable 16 and has a bananatype connector plug 130 at the other end thereof contained within a boreextending through block 118. Plug 130 is received in a mating jack 132,one end of which is threadably received within a counterbore on the sideof block 118 opposite tube 126 and whose other end is threadablyreceived in a bored opening in a polystyrene tube 134 which is seated inshallow counterbores provided in the adjacent faces of blocks 116 and118, as shown. Tube 134 contains the high voltage contact 28 of thecircuit breaker, which contact is spaced from jack 132 by spring 136,and is adapted to contact one end 138 of the piston 30. The end 138 ofthe piston 30 extends through a bore in block 116 and into the bore oftube 134, substantially as shown.

This piston is slidably contained within the conducting cylinder 32 theopposite ends of which are seated in annular grooves provided inadjacent faces of support blocks 114, 116. Piston 30 is shown as havingan enlarged central portion 30a, which is piloted within the cylinder32, and a reduced end portion 140 which is adapted to enter and slide ina bore extending through block 114. Seated in shallow counterboresformed in adjacent faces of blocks 114 and 112 is another polystyrenetube 144 which mounts the spring biased ground contact 34 that isconnected to ground over conducting bus 36. The support blocks and tubesof the breaker assembly are rigidly secured together as by tie bolts 148and 149.

The walls 150 of the breaker housing 110 receives the air inlet line 40through an opening therein adjacent the inlet to the air valve 42, whichmay be a type EV-SA Electroaire four-way valve operated from a 110 v.-10v. step-down transformer as manufactured by the Bellows ManufacturingCompany, of Akron, Ohio. The two outlets of the valve are connected byappropriate lengths of rubber hose or flexible tubing 44 and 46 toopenings 154 and 156 in the cylinder 32 on opposite sides of the piston30. The air inlet line 40 may be provided with an appropriate shut-oftcock valve, filter, pressure reducer, pressure gauge and lubricator inaccordance with conventional practice.

As shown in Fig. 4, the cylinder 32 is conductively connected by abanana plug and jack 160 to a conductor 162, which extends centrallythrough a polystyrene tube 164 and is connected to a coaxial cableconnector 166 contained in the front wall 168 of the cabinet housing.Connector 166 is connected to the coaxial cable 20 lead.- ing rear ardlyto the needle-like discharge electrodes 96 of the charging systemlocated at the gun.

In the operation of the system, inward movement of the trigger 77 by theoperator initiates the flow of paint in atomized spray form from the gunand completes an energizing circuit for the coil 64 of the control relay54 from the low voltage section of the power supply. Energization of therelay closes contact 61 and opens contact 62 thereof to complete a lowvoltage energizing circuit from the secondary of transformer 56 overconductor 50 to the advance coil or upper section of the solenoid 48 invalve 42, which is then actuated to supply air from line 40 to airhose44 communicating with the left side of the fir piston 30 in the cylinder32 and causes the piston to move rapidly to the right to engage highvoltage contact 28. This completes the high potential circuit for theelectrodes of the particle charging system from the output of the powersupply 10, conductor 16, breaker contact 28, piston 30, cylinder 32,coaxial cable 20, the discharge needles 96, the ionized zone betweendischarge needles and the collector plate 94, and back to the powersupply over conductor 24. When the trigger of the spray gun is released,the actuating coil of relay 54 is de-energized, which causes relaycontacts 61 to open and contacts 62 to close, the latter establishing anenergizing circuit for the retract or lower section of the solenoid coil42. Air is then supplied to the right side of the breaker piston whichthen moves to the left to break the circuit at contact 28.

Since the coaxial cable 20 from the breaker to the discharge electrodesof the particle charging system carried by the spray gun may be ofconsiderable length, a substantial amount of high potential energy willbe stored within the coaxial cable by the capacitance efiect thereof.This energy will remain on the cable for some time even after the systemhas been disconnected from the 110 v. line. So that the operator maysafely handle the electrodes, as for example when it is desired todisassemble the charger from the gun for cleaning after a period of use,the breaker of the present invention provides for rapid dissipation ofthe energy stored on the cable by connecting the cable 20 to groundthrough the cylinder 32, piston 30 and ground contact 34 when thetrigger 77 is released.

It will be noted also that the breaker 18, which is of the S.P.D.T.variety, is located in the output of the high tension power supply andthat its operation will not afiect the condition of energization of thepower supply which will be ready to deliver its full-rated output at alltimes and differs from those installations in which the entire powersupply unit is de-energized to control the application and interruptionof the high tension voltage to the electrodes of the charging ordepositing system.

What is claimed is:

1. In an electrostatic coating installation for spraying an article tobe coated and including an electrically grounded spray gun projectingparticles of coating material for deposition on said article, meansenhancing the deposition of said particles including discharge electrodemeans between said spray gun and said article and power supply meanssupplying a high tension output voltage to maintain said dischargeelectrode means at a high absolute potential relative to ground, thecombination of a high tension circuit breaker having amovable operatingmember directly electrically connected to said discharge electrode meansand operable between a pair of contact positions one of which iselectrically connected to the output of said power supply means and theother to ground, and means controlling the operation of said circuitbreaker.

2. In an electrostatic coating installation for spraying an article tobe coated and including an electrically grounded spray gun projectingparticles of coating material for deposition on said article, meansenhancing the deposition of said particles including discharge electrodemeans between said spray gun and said article and power supply meanssupplying a high tension output voltage to maintain said dischargeelectrode means at a high absolute potential relative to ground, thecombination of a high tension circuit breaker having an operating membermovable between a pair of contact positions and a coaxial cable directlyconnecting said movable operating member to said discharge electrodemeans, said operating member being connected in one of said contactpositions to the output of said power supply means and in the othercontact position to ground.

3. In an electrostatic spray coating installation for spraying anarticle to be coated, the combination of a spray gun projectingparticles of coating material in a path directed generally toward saidarticle for deposition thereon, means enhancing the deposition of saidparticles on said article including discharge electrode means andcurrent collector electrode means on the opposite sides of the path ofsaid particles projected from said spray gun and located between thespray gun and the articleto be coated, power supply means supplying ahigh tension output voltage for application between said dischargeelectrode means and said current collector electrode means, high tensioncircuit breaker means connected in circuit controlling relation in theoutput of said power supply and connected directly to said dischargeelectrode means, control means for said circuit breaker including aremote control element located at said gun and a common operating memberon said gun for controlling both the fiow of particles projected fromthe gun and the remote operation of said circuit breaker.

4. In an electrostatic spray coating installation for spraying anarticle to be coated, the combination of a spray gun projectingparticles of coating material in a path directed generally toward saidarticle for deposition thereon, means enhancing the deposition of saidparticles on said article including discharge electrode means andcurrent collector electrode means on opposite sidw of the path of saidparticles projected from said spray gun and located between the spraygun and the article to be coated, power supply means supplying a hightension output voltage for application between said dischargeele ctrodemeans and said current collector electrode means, a high tension circuitbreaker having a movable member electrically connected directly to saiddischarge electrode means and operable between a pair of contactpositions one of which is electrically connected in the high tensionoutput of said power sup-ply and the other to g round.

5. In an electrostatic spray coating installation for spraying anarticle to be coated, the combination of a hand spray gun manuallyoperable to project particl es of coating material in a path directedgenerally toward said article for deposition thereon, means enhancingthe deposition of said particles on said article including dischargeelectrode means and current collector electrode means on the oppositesides of the path of said particles projected from said spray gun andlocated between the spray gun and the article to be coated, insulatormeans mounting said discharge electrode means and said current collectorelectrode means on said spray gun, power supply means supplying a hightension output voltage for application between said discharge electrodemeans and said current collector electrode means, high tension circuitbreaker means connected in circuit controlling relation in the output ofsaid power supply to said discharge electrode means, control means forsaid circuit breaker including a remote control element located at saidgun and a common operating member on said gun for controlling both theflow of particles projected from the gun and the remote operation ofsaid circuit breaker.

6. In an electrostatic spray coating installation for spraying anarticle to be coated the combination of a spray gun having a gun bodyportion with a handle on one end and a spray tip nozzle on the other endfor projecting particles of coating material in a path directedgenerally toward said article for deposition thereon, means enhancingthe deposition of said particles on said article including dischargeelectrode means and current collector electrode means on the oppositesides of the path of said particles projected from said spray gun andlocated between the spray gun and the article to be coated, power supplymeans supplying a high tension output voltage for application betweensaid discharge electrode means and said current collector electrodemeans, a high tension circuit breaker connected in circuit controllingrelation in the output of said power supply and connected directly tosaid discharge electrode means, control means for said circuit breakerincluding a remote control element located at said gun and a commonopera ating member on said gun for controlling both the flow ofparticles projected from the gun and the remote operation of saidcircuit breaker, and an insulating shield mounted on the body of the gunbetween the handle and spray tip thereof and supporting said dischargeelectrode means and said current collector electrode means therefrom.

7. Electrostatic spray coating apparatus of the character described,comprising: spray discharging means having a portable body provided witha gripping handle, a spray control trigger member adjacent the handle,and a spray discharge portion spaced from the handle for projectingspray particles in a forwardly extending path; support means ofelectrically insulating material mounted on said portable body adjacentthe spray discharge portion thereof and extending on opposite sides ofsaid spray discharge portion; discharge electrode means mounted on saidsupport means forwardly of said spray discharge portion on one side ofthe path of particles projected therefrom; current collector electrodemeans mounted on said support means forwardly of said spray dischargeportion and opposite said discharge electrode means on the other side ofthe path of projected particles; a power supply for providing a highvoltage electrical field be tween the discharge electrode means and thecollector electrode means; a high tension circuit breaker having amovable operating member directly electrically connected to saiddischarge electrode means and operable between a pair of contactpositions, one of which is electrically connected to the output of saidpower supply and the other to ground; and control means for said circuitbreaker including a remote control element mounted on the body of thespray discharging means and operably connected to said trigger memberwhereby said trigger member controls both the flow of particlesprojected from thespray discharging means and the remote operation ofsaid circuit breaker means.

8. Electrostatic spray coating apparatus of the character described,comprising: a pistol-shaped spray gun having a portable body providedwith a gripping handle, a

spray control trigger member adjacent the handle, and a spray nozzlespaced from the handle for projecting spray particles in a forwardlyextending path; support means of electrically insulating materialmounted on said portable body adjacent the nozzle and extending onopposite sides of the nozzle; discharge electrode means mounted on saidsupport means forwardly of said nozzle on one side of the path ofparticles projected therefrom; current collector electrode means mountedon said support means forwardly of said nozzle and opposite saiddischarge electrode means on the other side of the path of particlesprojected from the nozzle; a power supply for providing a high voltageelectrical field between the discharge electrode means and the collectorelectrode means; a high tension circuit breaker having a movableoperating member directly electrically connected to said dischargeelectrode means and operable between a pair of contact positions, one ofwhich is electrically connected to the output of said power supply andthe other to ground; and control means for the circuit breaker includinga remote control element supported on the body of the spray gun andoperably connected to said trigger whereby said trigger controls boththe flow of particles projected from the spray gun and also controls theoperation of the circuit breaker.

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